Electro-optic display backplane structures with drive components and pixel electrodes on opposed surfaces

ABSTRACT

This invention relates to an electro-optic display having a backplane with a front surface and a reverse surface on opposed sides of the backplane, a front surface having a plurality of pixel electrodes arranged in a matrix of columns and rows with column and row lines, a reverse surface having at least one driver chip, and conductive vias electrically connecting the column and row lines on the front surface to the driver chip on the reverse surface, such that the entire front surface area may be optically active.

REFERENCE TO RELATED APPLICATIONS

The entire contents of this copending application, and of all other U.S.patents and published and copending applications mentioned below, areherein incorporated by reference.

BACKGROUND OF INVENTION

In applications where individual electro-optic displays are tiledtogether to create a larger display, it is optimal for the viewing areato be completely active. Accordingly, this invention relates to anelectro-optic display having a backplane with circuit elements on atleast two surfaces, a plurality of pixels arranged in a matrix on thefront surface of the backplane, at least one driver chip on the reversesurface (opposite the front surface of the backplane), and conductorsconnecting the plurality of pixels on the front surface to the driverchip on the reverse surface, such that the entire viewing surface areamay be optically active.

The term “electro-optic”, as applied to a material or a display, is usedherein in its conventional meaning in the imaging art to refer to amaterial having first and second display states differing in at leastone optical property, the material being changed from its first to itssecond display state by application of an electric field to thematerial. Although the optical property is typically color perceptibleto the human eye, it may be another optical property, such as opticaltransmission, reflectance, luminescence or, in the case of displaysintended for machine reading, pseudo-color in the sense of a change inreflectance of electromagnetic wavelengths outside the visible range.

Some electro-optic materials are solid in the sense that the materialshave solid external surfaces, although the materials may, and often do,have internal liquid- or gas-filled spaces. Such displays using solidelectro-optic materials may hereinafter for convenience be referred toas “solid electro-optic displays”. Thus, the term “solid electro-opticdisplays” includes rotating bichromal member displays, encapsulatedelectrophoretic displays, microcell electrophoretic displays andencapsulated liquid crystal displays.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin U.S. Pat. No. 7,170,670 that some particle-based electrophoreticdisplays capable of gray scale are stable not only in their extremeblack and white states but also in their intermediate gray states, andthe same is true of some other types of electro-optic displays. Thistype of display is properly called “multi-stable” rather than bistable,although for convenience the term “bistable” may be used herein to coverboth bistable and multi-stable displays.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedby applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display uses an electrochromic medium, forexample an electrochromic medium in the form of a nanochromic filmcomprising an electrode formed at least in part from a semi-conductingmetal oxide and a plurality of dye molecules capable of reversible colorchange attached to the electrode; see, for example O'Regan, B., et al.,Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24(March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845.Nanochromic films of this type are also described, for example, in U.S.Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium isalso typically bistable.

Another type of electro-optic display is an electro-wetting displaydeveloped by Philips and described in Hayes, R. A., et al., “Video-SpeedElectronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003).It is shown in U.S. Pat. No. 7,420,549 that such electro-wettingdisplays can be made bistable.

One type of electro-optic display, which has been the subject of intenseresearch and development for a number of years, is the particle-basedelectrophoretic display, in which a plurality of charged particles movethrough a fluid under the influence of an electric field.Electrophoretic displays can have attributes of good brightness andcontrast, wide viewing angles, state bistability, and low powerconsumption when compared with liquid crystal displays. Nevertheless,problems with the long-term image quality of these displays haveprevented their widespread usage. For example, particles that make upelectrophoretic displays tend to settle, resulting in inadequateservice-life for these displays.

As noted above, electrophoretic media require the presence of a fluid.In most prior art electrophoretic media, this fluid is a liquid, butelectrophoretic media can be produced using gaseous fluids; see, forexample, Kitamura, T., et al., “Electrical toner movement for electronicpaper-like display”, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y.,et al., “Toner display using insulative particles chargedtriboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also U.S. Pat.Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic mediaappear to be susceptible to the same types of problems due to particlesettling as liquid-based electrophoretic media, when the media are usedin an orientation which permits such settling, for example in a signwhere the medium is disposed in a vertical plane. Indeed, particlesettling appears to be a more serious problem in gas-basedelectrophoretic media than in liquid-based ones, since the lowerviscosity of gaseous suspending fluids as compared with liquid onesallows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporationdescribe various technologies used in encapsulated electrophoretic andother electro-optic media. Such encapsulated media comprise numeroussmall capsules, each of which itself comprises an internal phasecontaining electrophoretically-mobile particles in a fluid medium, and acapsule wall surrounding the internal phase. Typically, the capsules arethemselves held within a polymeric binder to form a coherent layerpositioned between two electrodes. The technologies described in thesepatents and applications include:

(a) Electrophoretic particles, fluids and fluid additives; see forexample U.S. Pat. Nos. 7,002,728 and 7,679,814;

(b) Capsules, binders and encapsulation processes; see for example U.S.Pat. Nos. 6,922,276 and 7,411,719;

(c) Films and sub-assemblies containing electro-optic materials; see forexample U.S. Pat. Nos. 6,982,178 and 7,839,564;

(d) Backplanes, adhesive layers and other auxiliary layers and methodsused in displays; see for example U.S. Pat. Nos. D485,294; 6,124,851;6,130,773; 6,177,921; 6,232,950; 6,252,564; 6,312,304; 6,312,971;6,376,828; 6,392,786; 6,413,790; 6,422,687; 6,445,374; 6,480,182;6,498,114; 6,506,438; 6,518,949; 6,521,489; 6,535,197; 6,545,291;6,639,578; 6,657,772; 6,664,944; 6,680,725; 6,683,333; 6,724,519;6,750,473; 6,816,147; 6,819,471; 6,825,068; 6,831,769; 6,842,167;6,842,279; 6,842,657; 6,865,010; 6,967,640; 6,980,196; 7,012,735;7,030,412; 7,075,703; 7,106,296; 7,110,163; 7,116,318; 7,148,128;7,167,155; 7,173,752; 7,176,880; 7,190,008; 7,206,119; 7,223,672;7,230,751; 7,256,766; 7,259,744; 7,280,094; 7,327,511; 7,349,148;7,352,353; 7,365,394; 7,365,733; 7,382,363; 7,388,572; 7,442,587;7,492,497; 7,535,624; 7,551,346; 7,554,712; 7,583,427; 7,598,173;7,605,799; 7,636,191; 7,649,674; 7,667,886; 7,672,040; 7,688,497;7,733,335; 7,785,988; 7,843,626; 7,859,637; 7,893,435; 7,898,717;7,957,053; 7,986,450; 8,009,344; 8,027,081; 8,049,947; 8,077,141;8,089,453; 8,208,193; and 8,373,211; and U.S. Patent ApplicationsPublication Nos. 2002/0060321; 2004/0105036; 2005/0122306; 2005/0122563;2007/0052757; 2007/0097489; 2007/0109219; 2007/0211002; 2009/0122389;2009/0315044; 2010/0265239; 2011/0026101; 2011/0140744; 2011/0187683;2011/0187689; 2011/0286082; 2011/0286086; 2011/0292319; 2011/0292493;2011/0292494; 2011/0297309; 2011/0310459; and 2012/0182599; andInternational Application Publication No. WO 00/38000; European PatentsNos. 1,099,207 B1 and 1,145,072 B1;

(e) Color formation and color adjustment; see for example U.S. Pat. No.7,075,502; and U.S. Patent Application Publication No. 2007/0109219;

(f) Methods for driving displays; see for example U.S. Pat. Nos.7,012,600 and 7,453,445;

(g) Applications of displays; see for example U.S. Pat. Nos. 7,312,784and 8,009,348; and

(h) Non-electrophoretic displays, as described in U.S. Pat. Nos.6,241,921; 6,950,220; 7,420,549 and 8,319,759; and U.S. PatentApplication Publication No. 2012/0293858.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display, inwhich the electrophoretic medium comprises a plurality of discretedroplets of an electrophoretic fluid and a continuous phase of apolymeric material, and that the discrete droplets of electrophoreticfluid within such a polymer-dispersed electrophoretic display may beregarded as capsules or microcapsules even though no discrete capsulemembrane is associated with each individual droplet; see for example,the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes ofthe present application, such polymer-dispersed electrophoretic mediaare regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to SipixImaging, Inc.

Although electrophoretic media are often opaque (since, for example, inmany electrophoretic media, the particles substantially blocktransmission of visible light through the display) and operate in areflective mode, many electrophoretic displays can be made to operate ina so-called “shutter mode” in which one display state is substantiallyopaque and one is light-transmissive. See, for example, U.S. Pat. Nos.5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and6,184,856. Dielectrophoretic displays, which are similar toelectrophoretic displays but rely upon variations in electric fieldstrength, can operate in a similar mode; see U.S. Pat. No. 4,418,346.Other types of electro-optic displays may also be capable of operatingin shutter mode. Electro-optic media operating in shutter mode may beuseful in multi-layer structures for full color displays; in suchstructures, at least one layer adjacent the viewing surface of thedisplay operates in shutter mode to expose or conceal a second layermore distant from the viewing surface.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating; meniscus coating; spin coating; brush coating; air knifecoating; silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink-jet printing processes;electrophoretic deposition (See U.S. Pat. No. 7,339,715); and othersimilar techniques.) Thus, the resulting display can be flexible.Further, because the display medium can be printed (using a variety ofmethods), the display itself can be made inexpensively.

Other types of electro-optic materials may also be used in the presentinvention. Of particular interest, bistable ferroelectric liquid crystal(FLC's) and cholesteric liquid crystal displays are known in the art.

An electrophoretic display normally comprises a layer of electrophoreticmaterial and at least two other layers disposed on opposed sides of theelectrophoretic material, one of these two layers being an electrodelayer. In most such displays both the layers are electrode layers, andone or both of the electrode layers are patterned to define the pixelsof the display. For example, one electrode layer may be patterned intoelongate row electrodes and the other into elongate column electrodesrunning at right angles to the row electrodes, the pixels being definedby the intersections of the row and column electrodes. Alternatively,and more commonly, one electrode layer has the form of a singlecontinuous electrode and the other electrode layer is patterned into amatrix of pixel electrodes, each of which defines one pixel of thedisplay. In another type of electrophoretic display, which is intendedfor use with a stylus, print head or similar movable electrode separatefrom the display, only one of the layers adjacent the electrophoreticlayer comprises an electrode, the layer on the opposed side of theelectrophoretic layer typically being a protective layer intended toprevent the movable electrode damaging the electrophoretic layer.

The manufacture of a three-layer electrophoretic display normallyinvolves at least one lamination operation. For example, in several ofthe aforementioned MIT and E Ink patents and applications, there isdescribed a process for manufacturing an encapsulated electrophoreticdisplay in which an encapsulated electrophoretic medium comprisingcapsules in a binder is coated on to a flexible substrate comprisingindium-tin-oxide (ITO) or a similar conductive coating (which acts asone electrode of the final display) on a plastic film, thecapsules/binder coating being dried to form a coherent layer of theelectrophoretic medium firmly adhered to the substrate. Separately, abackplane, containing an array of pixel electrodes and an appropriatearrangement of conductors to connect the pixel electrodes to drivecircuitry, is prepared. To form the final display, the substrate havingthe capsule/binder layer thereon is laminated to the backplane using alamination adhesive. (A very similar process can be used to prepare anelectrophoretic display usable with a stylus or similar movableelectrode by replacing the backplane with a simple protective layer,such as a plastic film, over which the stylus or other movable electrodecan slide.) In one preferred form of such a process, the backplane isitself flexible and is prepared by printing the pixel electrodes andconductors on a plastic film or other flexible substrate. The obviouslamination technique for mass production of displays by this process isroll lamination using a lamination adhesive.

As discussed in the aforementioned U.S. Pat. No. 6,982,178, (see column3, line 63 to column 5, line 46) many of the components used inelectrophoretic displays, and the methods used to manufacture suchdisplays, are derived from technology used in liquid crystal displays(LCD's). For example, electrophoretic displays may make use of abackplane comprising an array of transistors or diodes and acorresponding array of pixel electrodes, and a “continuous” frontelectrode (in the sense of an electrode which extends over multiplepixels and typically the whole display) on a transparent substrate,these components being essentially the same as in LCD's. However, themethods used for assembling LCD's cannot be used with encapsulatedelectrophoretic displays. LCD's are normally assembled by forming thebackplane and front electrode on separate glass substrates, thenadhesively securing these components together leaving a small aperturebetween them, placing the resultant assembly under vacuum, and immersingthe assembly in a bath of the liquid crystal, so that the liquid crystalflows through the aperture between the backplane and the frontelectrode. Finally, with the liquid crystal in place, the aperture issealed to provide the final display.

This LCD assembly process cannot readily be transferred to encapsulateddisplays. Because the electrophoretic material is solid, it must bepresent between the backplane and the front electrode before these twointegers are secured to each other. Furthermore, in contrast to a liquidcrystal material, which is simply placed between the front electrode andthe backplane without being attached to either, an encapsulatedelectrophoretic medium normally needs to be secured to both; in mostcases the electrophoretic medium is formed on the front electrode, sincethis is generally easier than forming the medium on thecircuitry-containing backplane, and the front electrode/electrophoreticmedium combination is then laminated to the backplane, typically bycovering the entire surface of the electrophoretic medium with anadhesive and laminating under heat, pressure and possibly vacuum.Accordingly, most prior art methods for final lamination of solidelectrophoretic displays are essentially batch methods in which(typically) the electro-optic medium, a lamination adhesive and abackplane are brought together immediately prior to final assembly, andit is desirable to provide methods better adapted for mass production.

Electro-optic displays, including electrophoretic displays, can becostly; for example, the cost of the color LCD found in a portablecomputer is typically a substantial fraction of the entire cost of thecomputer. As the use of such displays spreads to devices, such ascellular telephones and personal digital assistants (PDA's), much lesscostly than portable computers, there is great pressure to reduce thecosts of such displays. The ability to form layers of electrophoreticmedia by printing techniques on flexible substrates, as discussed above,opens up the possibility of reducing the cost of electrophoreticcomponents of displays by using mass production techniques such asroll-to-roll coating using commercial equipment used for the productionof coated papers, polymeric films and similar media.

Whether a display is reflective or transmissive, and whether or not theelectro-optic medium used is bistable, to obtain a high-resolutiondisplay, individual pixels of a display must be addressable withoutinterference from adjacent pixels. One way to achieve this objective isto provide an array of non-linear elements, such as transistors ordiodes, with at least one non-linear element associated with each pixel,to produce an “active-matrix” display. An addressing or pixel electrode,which addresses one pixel, is connected to an appropriate voltage sourcethrough the associated non-linear element. Typically, when thenon-linear element is a transistor, the pixel electrode is connected tothe drain of the transistor, and this arrangement will be assumed in thefollowing description, although it is essentially arbitrary and thepixel electrode could be connected to the source of the transistor.Conventionally, in high resolution arrays, the pixels are arranged in atwo-dimensional array of rows and columns, such that any specific pixelis uniquely defined by the intersection of one specified row and onespecified column. The sources of all the transistors in each column areconnected to a single column electrode, while the gates of all thetransistors in each row are connected to a single row electrode; againthe assignment of sources to rows and gates to columns is conventionalbut essentially arbitrary, and could be reversed if desired. The rowelectrodes are connected to a row driver, which essentially ensures thatat any given moment only one row is selected, i.e., that there isapplied to the selected row electrode a voltage such as to ensure thatall the transistors in the selected row are conductive, while there isapplied to all other rows a voltage such as to ensure that all thetransistors in these non-selected rows remain non-conductive. The columnelectrodes are connected to column drivers, which place upon the variouscolumn electrodes voltages selected to drive the pixels in the selectedrow to their desired optical states. (The aforementioned voltages arerelative to a common front electrode, which is conventionally providedon the opposed side of the electro-optic medium from the non-lineararray and extends across the whole display.) After a pre-selectedinterval known as the “line address time” the selected row isdeselected, the next row is selected, and the voltages on the columndrivers are changed to that the next line of the display is written.This process is repeated so that the entire display is written in arow-by-row manner.

Processes for manufacturing active-matrix displays are well established.Thin-film transistors, for example, can be fabricated using variousdeposition and photolithography techniques. A transistor includes a gateelectrode, an insulating dielectric layer, a semiconductor layer andsource and drain electrodes. Application of a voltage to the gateelectrode provides an electric field across the dielectric layer, whichdramatically increases the source-to-drain conductivity of thesemiconductor layer. This change permits electrical conduction betweenthe source and the drain electrodes. Typically, the gate electrode, thesource electrode, and the drain electrode are patterned. In general, thesemiconductor layer is also patterned in order to minimize strayconduction (i.e., cross-talk) between neighboring circuit elements.

Electro-optic displays are often used to form large area displays, forexample in the form of large signs or billboards. Such large areadisplays are frequently formed by “tiling” (i.e., juxtaposing) atwo-dimensional array of discrete electro-optic displays together since,for technical reasons, such as limitations on the size of backplanesproduced by photolithography, individual electro-optic displays cannoteconomically exceed a certain size. To create the illusion of a singlelarge area display, it is important that the whole visible area of thedisplay be active, with no inactive borders between adjacent displays.Unfortunately, conventional electro-optic displays require driverelectronics which are normally disposed around the periphery of thedisplay. Such peripheral driver electronics are not a problem whendisplays are used individually, since the active area of the display isnormally surrounded by a bezel which serves to hide the driverelectronics. However, such peripheral driver electronics do create aproblem when multiple displays are used to form a large area displaysince the peripheral areas are inherently optically inactive.Accordingly, there is a need a way of tiling electro-optic displaystogether to form large area displays without introducing inactive areasin peripheral portions of the individual displays.

SUMMARY OF INVENTION

Accordingly, this invention relates to an electro-optic display having abackplane with a front surface and a reverse surface on opposed sides ofthe backplane, the front surface having a plurality of pixel electrodesarranged in a matrix of rows and columns having row and columns lineswith conductive vias at each row and column line, and the reversesurface having at least one driver chip connecting to the conductivevias at each row and column line, wherein the plurality of pixelelectrodes on the front surface are electrically connected to the driverchip on the reverse surface, such that the entire viewing surface areamay be optically active.

In another aspect, this invention provides for a backplane for anelectro-optic display comprising a first major surface having aplurality of pixel electrodes arranged in an array of rows and columnshaving row and column lines, a second major surface opposed to the firstmajor surface having at least two driver chips, and a plurality ofconductive vias at each row line and each column line to electricallyconnect the row lines to the first driver chip and the column lines tothe second driver chip.

In another aspect, this invention provides for an electro-optic assemblycontaining a backplane having a plurality of pixel electrodes on thefront surface, at least one driver on the reverse surface and electricalconnections between the pixel electrodes and the driver, such thatalmost 100% of the viewing surface may be optically active.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic circuit diagram of one pixel of an active matrixelectro-optic display according to some embodiments.

FIG. 2 is a top plan view showing a single pixel of the viewing surfaceof a display according to some embodiments.

FIG. 3 is a top plan view of the front surface of a backplane of thepresent invention having a 5×5 pixel array.

FIG. 4 is a plan view of the reverse surface of the backplane shown inFIG. 3 a single driver and connections thereto.

FIG. 5 is a plan view similar to that of FIG. 4 but is an embodimentshowing two drivers and connections thereto.

FIG. 6 is an illustrative representation of the present invention usedin a large scale sign.

DETAILED DESCRIPTION

The use of electro-optic display technology is expanding beyondelectronic document reader applications to a variety of electronicdisplay products including product labels, retail shelf labels, devicemonitoring indicators, wristwatches, signs, and promotional oradvertising displays. Typically, electro-optic displays are encased by aframe or a bezel to hide the electrical connections of the display whichgenerally lay alongside the display. In some applications, specifically,large scale tiled displays, it is generally preferred that the entireviewing area of an electro-optic display be optically active; forexample, a billboard made by tiling a plurality of electro-opticdisplays together to create a large display, where the entire viewingsurface of each individual display is optically active and the spacebetween each display is minimized, such that the large display appearsas a single continuous display.

Accordingly, this invention provides for an electro-optic display havinga backplane with circuit elements on at least two surfaces, a pluralityof pixel electrodes arranged in an array of rows and columns on thefront surface of the backplane having row and column lines, at least onedriver chip on the reverse surface (opposite the front surface of thebackplane), and conductive vias connecting the row and column lines ofthe plurality of pixel electrodes on the front surface to the driverchip on the reverse surface, such that the entire viewing surface areamay be optically active.

In another aspect, this invention provides for an electro-optic displayhaving a backplane with two major surfaces wherein a first major surfacehas a plurality of pixel electrodes, and a second major surface opposedto the first major surface has at least one driver chip, a plurality ofgate lines with a conductive via for each gate line, a plurality ofsource lines with a conductive via for each source line, a plurality ofcommon lines with at least one conductive via to electrically connectthe plurality of pixel electrodes to the driver chip, such that theentire viewing surface area may be optically active.

In another aspect, this invention provides for an electro-optic assemblycontaining a backplane having a plurality of pixel electrodes on thefront surface, at least one driver on the reverse surface and electricalconnections between the pixel electrodes and the driver, such thatalmost 100% of the viewing surface may be optically active.

The term “backplane” is used herein consistent with its conventionalmeaning in the art of electro-optic displays and in the aforementionedpatents and published applications, to mean a rigid or flexible materialprovided with one or more electrodes. The backplane may also be providedwith electronics for addressing the display, or such electronics may beprovided in a unit separate from the backplane. A backplane may containmultiple layers. A backplane may be referred to as a rear electrodestructure. The front surface of a backplane refers to the surfaceclosest to the front electrode of the display. The reverse surface of abackplane refers to the surface farthest from the front electrode.

The term “viewing surface” is used herein consistent with itsconventional meaning in the art of electro-optic displays and in theaforementioned patents and published applications, to mean the surfaceclosest to the front electrode (the surface remote from the backplane).

The term “non-viewing surface” is used herein to mean any surface orside that is not the viewing surface. This includes the reverse side ofa backplane, the sides of a backplane and, if multi-layered, any layerof the backplane that is not on the viewing surface.

Typically, a backplane has an array of pixel electrodes. Each pixelelectrode forms part of a “pixel unit” which usually also includes athin-film transistor, a storage capacitor, and conductors thatelectrically connect each pixel unit to a driver chip. Although a pixelelectrode is technically a subpart of a pixel unit, the terms “pixel”and “pixel electrode” are commonly used interchangeably and refer to aunit cell of a backplane active area. The terms “column lines” and “rowlines” generally refer to the “gate lines” and “source lines” of a pixeltransistor. These terms are used interchangeably herein.

FIG. 1 is an illustrative schematic of the circuitry of a type of singlethin film transistor pixel (100), including a pixel electrode (105), acapacitor electrode (104), a thin-film transistor (106), a gate line(103), a source line (101) and a common (ground) line (102). The sourceline (101) is connected to the source of the transistor (106), the gateline (103) is connected to the gate of the transistor (106) and thedrain of the transistor (106) is connected to the pixel electrode (105).The capacitor electrode (104) is connected to the ground line (102) sothat the pixel electrode (105) and the capacitor electrode (104)together form a storage capacitor (107).

FIG. 2 is an illustrative schematic of the present invention of a singlepixel including a pixel electrode (105), a capacitor electrode (104), athin-film transistor (106), a gate line (103), a source line (101) and acommon (ground) line (102). Conductive vias at each gate line (201) andat each source line (200) electrically connect the pixel electrode tothe driver on the reverse surface of the backplane. A conductive via(203) connects the ground lines (102) to the driver on the reversesurface.

The thin-film transistor of the pixel electrode may be electricallyconnected to the driver chip by formation of via apertures through thebackplane. The apertures may be filled with conductive material to formvias interconnecting electronic components on the viewing side toelectronic components on the reverse side of the backplane. The viaapertures may be, for example, etched, punched, drilled or laser-drilledthrough the polymeric material of the backplane so as to connect theelectronic components on the viewing side to the drivers on the reverseside. The via apertures may be filled using a variety of materials andtechniques including printing (for example, ink-jet, screen, or offsetprinting) application of conductive resins, shadow-mask evaporation orconventional photolithographic methods. Simple electrical connectionsmay be made along the edge of the substrate using thick film conductors.

FIG. 3 is an illustrative schematic of a 5×5 array of pixels of abackplane of the present invention which includes pixel electrodes(105), capacitor electrodes (104), thin-film transistors (106), gatelines (103), source lines (101), common (ground) lines (102), sourceline conductive vias (200), gate line conductive vias (201) and a commonline conductive via (203). The pixel components are layered orsandwiched between semiconductor layers to provide electricalconnections and prevent cross-talk between neighboring components. Thepixel electrode, usually, is on the front surface of the backplane andis the closest layer to the viewing surface. The electro-optic layerattaches to the pixel electrode layer such that, essentially, the entireviewing surface is optically active. The pixel electrode layer may belight transmissive when the electro-optic layer acts to mask theunderlying components on the backplane.

The array of transistors shown in FIG. 3 can be manufactured using anyone of many appropriate methods. For example, vacuum based methods suchas evaporation or sputtering can be used to deposit the materialsnecessary to form the transistor and thereafter the deposited materialcan be patterned. Alternatively, wet printing methods or transfermethods can be used to deposit the materials necessary to form thetransistors. For fabrication of thin-film transistors, the substrate maybe, for example: a silicon wafer; a glass plate; a steel foil; or aplastic sheet. The gate electrodes, for example, may be any conductivematerial such as metal or conductive polymer. The materials for use asthe semiconductor layer, for example, can be inorganic materials such asamorphous silicon or polysilicon. Alternatively, the semiconductor layermay be formed of organic semiconductors such as: polythiophene and itsderivatives; oligothiophenes; and pentacene. In general, anysemiconductive material useful in creating conventional thin filmtransistors can be used in this embodiment. The material for the gatedielectric layer may be an organic or an inorganic material. Examples ofsuitable materials include, but are not limited to, polyimides, silicondioxide, and a variety of inorganic coatings and glasses. The source andgate electrodes may be made of any conductive material such as metal orconductive polymer.

The array of transistors described in reference to FIG. 3 may be anytype of transistors used for addressing an electronic display.Additional (i.e., resistors) or alternative (i.e., capacitors andtransistors) drive components may be used as well. In anotherimplementation, the addressing electronic backplane could incorporatediodes as the nonlinear element, rather than transistors. The presentinvention is applicable to a variety of electronic displays, includingelectrophoretic displays, liquid crystal displays, emissive displays(including organic light emitting materials) and rotating ball displays.

Alternatively, a passive matrix backplane rather than an active matrixbackplane may be used to drive the display. As is well-known in the art,a passive matrix backplane uses two sets of elongate electrodesextending at right angles to display an image on the screen. Each pixelis defined by the intersection of two electrodes, one from each set. Byaltering the electrical charge at a given intersection, theelectro-optic properties of the corresponding pixel may be changed.

FIG. 4 is an illustrative schematic of a reverse surface of a backplaneof the present invention showing a driver (400), conductive vias (200,201, 203) and conductors (401, 402) connecting the pixels in a 5×5 arrayon the front surface to the driver on the reverse surface. FIG. 4 showsthe conductive vias located at the end of each column and row accordingto the preferred embodiment, however, the vias may be located anywherealong the gate and source lines to make the electrical connection.

FIG. 4 illustrates a plan view of the conductive leads and the elementsfor an array of transistors for driving a display. An array comprisessource lines and gate lines with conductive vias connecting a driver topixel electrodes. To address a pixel electrode, voltages are applied toappropriate source lines and gate lines. Changes in the opticalcharacteristics of a display element are achieved by addressing a pixelelectrode that is associated with the display element.

From the foregoing, it will be seen that the present invention providesfor an electro-optic assembly containing a backplane having a pluralityof pixels arranged in rows and columns on the front surface, at leastone driver on the reverse surface and electrical connections between therow and column lines of the pixel array and the driver, such that 100%of the viewing surface may be optically active.

Display size and resolution may be optimized according to theelectro-optic display application, substrate materials and PCB designguidelines. Pixel size may vary from approximately 100 μm to more than10 mm per side (approximately 10,000 μm² to 100 mm²). Conductive viasmay range in size from 25 μm to 250 μm depending on the pixel size ofthe display. Individual display sizes may range from as large asmultiple feet squared to as small as less than an inch squared. Forlarge scale displays with a large viewing distance, a larger pixel sizeis preferred. For example, a billboard display may be constructed fromindividual displays of approximately 400 mm×400 mm with 4 mm×4 mm pixelsand conductive vias that are approximately 250 μm. For large scaledisplays with a shorter viewing distance, a smaller pixel size ispreferred. For example, a wall display may be constructed fromindividual displays of approximately 200 mm×200 mm with 200 μm×200 μmpixels.

The number of driver chips may be optimized according to design rules.At least one driver chip may be used. Preferably, at least two driverchips are used; one to drive the gate lines and one to drive the sourcelines.

FIG. 5 is an illustrative schematic of the present invention showing twodrivers (500, 501), conductive vias to the source lines (200) and gatelines (201), a conductive via to the common lines (203) and conductors(401, 402) connecting the pixels in a 5×5 array on the front surface tothe driver on the reverse surface. One driver (500) addresses the sourcelines and the other driver (501) addresses the gate lines and commonlines.

In one aspect of the present invention, a thin-film transistor,capacitor electrode and pixel electrode may be fabricated on the frontsurface of the backplane while a driver and connecting gate and sourcelines (and any additional electronic components) are formed on theopposed surface, then the via apertures are formed, and finally the viaapertures are filled to form vias. Vias may be filled with a conductivesubstance, such as solder or conductive epoxy, or an insulatingsubstance, such as epoxy. Alternatively, the gate and source lines maybe formed on the front surface of the backplane. In another alternative,the substrate may be drilled and filled to form vias, then, the thinfilm transistor array is formed with the source and gate lines landingon (aligning with) the conductive vias.

In another alternative, the backplane may be formed by printing thesource lines, gates lines and thin film transistors on a substrate,then, drilling an filling conductive vias, then, covering the vias withdielectric and, finally, printing the pixel electrodes.

The backplane substrate material may be any suitable material thatallows for the fabrication of one or more via apertures, such aspolyester, polyimide, multilayered fiberglass, stainless steel, PET orglass. Holes are punched, drilled, abraded, or melted through whereconductive paths are desired, including through any dielectric layers asnecessary. Alternatively, the apertures may be formed on the backplanematerials prior to assembly and then aligned when assembled. Aconductive ink may be used to fabricate and fill the holes. The pixelelectrode may be printed using a conductive ink as is known in the art.The ink viscosity, as well as the aperture size and placement, may beoptimized so that the ink fills the apertures. When the reverse surfacestructures are printed, again using conductive ink, the holes are againfilled. By this method, the connection between the front and back of thesubstrate may be made automatically.

The backplane of the display may comprise a substrate having a thin-filmtransistor array on the front surface, conductive vias located at eachcolumn and row, a driver on the reverse surface of the substrate, andgate and source lines connecting the thin-film transistor array to thedriver.

Alternatively, a printed circuit board may be used as the rear electrodestructure. The front of the printed circuit board may have copper padsetched in the desired shape. The plated vias connect the electrode padsto an etched wire structure (or conductor) on the reverse surface of theprinted circuit board. The wires may be run to the reverse surface rearof the printed circuit board and a connection can be made using astandard connector such as a surface mount connector or using a flexconnector and anisotropic glue.

Alternatively, a flex circuit such a copper-clad polyimide may be usedfor the rear electrode structure. Printed circuit board may be made ofpolyimide, which acts both as the flex connector and as the substratefor the electrode structure. Rather than copper pads, electrodes may beetched into the copper covering the polyimide printed circuit board. Theplated through vias connect the electrodes etched onto the substrate therear of the printed circuit board, which may have an etched conductornetwork thereon (the etched conductor network is similar to the etchedwire structure).

Alternatively, the rear electrode structure can be made entirely ofprinted layers. A conductive layer can be printed onto the back of adisplay comprised of a clear, front electrode and a printable displaymaterial. A clear electrode may be fabricated from indium tin oxide orconductive polymers such as polyanilines and polythiophenes. Adielectric coating may be printed leaving areas for vias. Then, the backlayer of conductive ink may be printed. If necessary, an additionallayer of conductive ink can be used before the final ink structure isprinted to fill in the holes.

This technique for printing displays can be used to build the rearelectrode structure on a display or to construct two separate layersthat are laminated together to form the display. For example anelectronically active ink may be printed on an indium tin oxideelectrode. Separately, a rear electrode structure as described above canbe printed on a suitable substrate, such as plastic, polymer films, orglass. The electrode structure and the display element can be laminatedto form a display.

Moreover, the encapsulated electrophoretic display is highly compatiblewith flexible substrates. This enables high-resolution thin-filmtransistor displays in which the transistors are deposited on flexiblesubstrates like flexible glass, plastics, or metal foils. The flexiblesubstrate used with any type of thin film transistor or other nonlinearelement need not be a single sheet of glass, plastic, metal foil,though. Instead, it could be constructed of paper. Alternatively, itcould be constructed of a woven material. Alternatively, it could be acomposite or layered combination of these materials.

FIG. 6 is an illustrative representation of the present invention usedin a large scale sign. The individual electro-optic displays (600) aretiled in a 5 by 4 array. The dotted lines (601) represent the edges ofthe individual displays. This figure shows a sign for a train stationthat displays icons and words (602) indicating the direction to thetrains.

The electro-optic display may have a front plane comprising, in orderbeginning from the backplane, a layer of electro-optic material disposedon the thin-film transistor array, a single continuous electrodedisposed on the electro-optic material and, optionally, a frontprotective layer or other barrier layers. The upper surface of theprotective layer forms the viewing surface of the display. An edge sealmay extend around the periphery of the electro-optic material to preventthe ingress of moisture to the electro-optic material.

In another aspect, this invention provides for an electro-optic displaywherein the electro-optic material masks the electrical connections suchthat the viewing surface may be completely optically-active. Theelectro-optic material of the front plane laminate may overlay the pixelelectrodes to obscure the backplane connections from the viewingsurface. In another aspect, the electro-optic material of the frontplane laminate may extend beyond the pixel electrodes to obscure thebackplane connections from the viewing surface.

In another aspect, as described in U.S. Pat. No. 8,705,164, frontelectrode connections may be on a non-viewing side of the backplane.Alternatively, front electrode connections may be made on the viewingsurface. Such connections create non-active areas on the viewingsurface. These non-active areas are usually approximately 2 mm indiameter but may be larger or smaller depending on the display voltagerequirements and the total number of connections. In comparison to theoverall active viewing area, the display may still appear to be 100%active. In the present invention, an active viewing area of at least 95%is preferred.

It will be apparent to those skilled in the art that numerous changesand modifications can be made in the specific embodiments of theinvention described above without departing from the scope of theinvention. Accordingly, the whole of the foregoing description is to beinterpreted in an illustrative and not in a limitative sense.

1. An electro-optic display having a backplane, the backplanecomprising: a first major surface comprising a plurality of pixelelectrodes arranged in an array of rows and columns having row andcolumn lines; a second major surface opposed to the first major surfacehaving at least one driver chip; and a plurality of conductive viaselectrically connecting the row lines of the pixel array to the driverchip.
 2. The display of claim 1 further comprising a plurality ofconductive vias electrically connecting the column lines of the pixelarray to the driver chip.
 3. The display of claim 1 further comprising:a second driver chip on the second major surface; and a plurality ofconductive vias electrically connecting the column lines of the pixelarray to the second driver chip.
 4. The display of claim 1, wherein thebackplane is a printed circuit board, a flex circuit, or a substrate ofprinted layers.
 5. The display of claim 1, wherein each of the pluralityof pixel electrodes has a thin-film transistor associated therewith. 6.The display of claim 1, wherein the pixel size is between 3 mm×3 mm and5 mm×5 mm.